Generally in a car, air ducts 52 connected to a number of ejecting openings 51 in communication with the interior of a car are provided to supply into the indoor space of a car either the air heated or cooled by a heater 57 or an air conditioner evaporator 55 or the fresh outside air, as shown in FIG. 1. Further, the air ducts 52 are provided with a number of dampers 53 to control the flow of the air supplied to the respective ejecting openings 51, wherein the dampers 53 are adjusted in their degree of opening by respective actuators feed-back controlled.
A conventional actuator for adjusting the opening of an air duct damper comprises, as shown in FIG. 2, a driving motor 10 brought into rotation by a control section, a power transmitting mechanism 20 connected to the driving motor 10 for transmitting a torque of the motor 10 to a damper 53, a connection terminal 61 provided at the power transmitting mechanism 20 and brought into rotation together with the power transmitting mechanism 20, a printed circuit board 60 attached on a case 65 and on which the connection terminal 61 is rotatable contacted. Further, as shown in FIG. 3, a printed variable resistance band 63 is provided at the bottom of the printed circuit board 60 and connected to different circuit pattern in accordance with the change of the contact position of the connection terminal 61.
Therefore, when a passenger causes the transmission of a signal to the control section by operating an inputting section installed on an instrument panel, the above-described driving motor 10 is brought into rotation in accordance with the signal of the control section, opening the damper 53 connected to the driving motor 10 through the power transmitting mechanism 20 at a predetermined rotation angle. And, the connection terminal 61 is disposed on one side of the power transmitting mechanism 20 so as to be rotated together with the power transmitting mechanism 20, and the connection terminal 61 is rotated in contact with the variable resistance band 63, so that the feed back signal about the rotation angle of the damper 53 can be transmitted to the control section.
However, there is a problem with such an actuator in that the opening of a damper 53 is difficult to exactly control, when the resistance value becomes erroneous due to the deposition of a foreign material on the variable resistance band 63 or the connection terminal 61, the change in the temperature or the like, because the rotation angle indicating the duct opening is sensed as the variation in the resistance depending on the contacting location between the connection terminal 61 and the variable resistance band 63. There is another problem of the decreased durability of the commodities, because easy wear takes place with the repeated operation as the result of the tight contact operation between the connection terminal 61 and the variable resistance band 63.
Moreover, there is still other disadvantage of the need for a separate interface circuitry, because the analog resistance signal representing the opening of a damper 53, as sensed, needs to be converted to a corresponding digital signal in order to be used for the feed back control of the driving motor 10.